While I fixed the problem on my road bike, the mountain bike is giving me a hard time.
The rear brakes are fine, but the front brakes, I may as well have a horn on the handlebar letting people know I am slowing down. The squeal occurs during the rolldown with either light pressure to slow or 100% pressure applied for hard (or full stop) braking.
Checking other threads lead to the sheldon brown site. Only primary troubleshooting was headset loose. Tested an appears tight. Plus squeaky brakes occurred both before and after the LBS repaired the RocShok Tora fork under warranty for some known damper/lockout issues with that fork - and re-assembly would require tightening the headset to spec if wasn't from the factory.
These are Shimano M485 hydraulic with 160 rotors.
I've done the following: 1) after 100 or so miles, torched the pads to burn off factory shipping oil or other contamination. 2) recently light sanding the pads (how I resolved the road bike issue) after washing the bike(s). 3) periodically try cleaning the rotor with moist hand towlettes. (4) pay attention to seating when mounting the wheel making sure the rotor is not angled between the pads.
Any suggestions? I am about at the point of getting new pads despite the relativeve newness (500-1000 miles) of the pads.